Leaf Dynamics and Shoot Production of the Seagrass Thalassia testudinum in the Indian River Lagoon (Florida)

Abstract

Leaf growth, biomass and production of Thalassia testudinum were measured from January 1995 to March 1996, for a monospecific population in the Indian River Lagoon (IRL; Florida). Seasonal pattern of shoot biomass was characterized by low values during late winter (minimum of 0.17 g dw shoot⁻¹ in March) and high values in mid-summer (July; 0.32 g dw shoot⁻¹). Production of new leaves followed a pattern similar to shoot biomass, although maximum production of leaves occurred slightly earlier (late May; 0.07 leaves shoot⁻¹ day⁻¹) than did maximum leaf elongation and biomass accumulation (July; 3.63 cm shoot⁻¹ day⁻¹ and 0.007 g dw shoot⁻¹ day⁻¹). Shoot densities (m⁻²) were low by the end of winter (390 ± 50.7 SE) and high in late summer (840 ± 201 SE), thus resulting in a measured standing stock variation between 197 and 328 g dw m⁻². Annual shoot production amounted to 890 g dw m⁻² and biomass turnover was 3.6. Compilation of data from the literature with results from this study showed T. testudinum leaf production was related to standing stock (p < 0.0001) by a factor of 0.016. Average daily production vs. biomass (P/B) slightly increased at lower latitudes. However, latitude only explained 34 % of the variation in P/B, other ecological factors (e. g. light or nutrient limitation) may play a major role in determining biomass and primary production for this species. Based on latitude alone, maximum potential production for Thalassia testudinum in the IRL (close to the northern limit of distribution for this species) would be up to 30 % lower than the values expected at the southern limit of distribution of this species.